(1) Field of the Invention
This invention relates to a differential mechanism for dividing and transmitting each torque from an input shaft to two output shafts, and particularly to a differential limiting device suitable for use in the differential mechanism.
(2) Description of the Prior Art
Differential limiting devices called LSDs (Limited Slip Differentials) have conventionally been proposed. In such an LSD, irrespective of the degree of difference in revolution speed between two output shafts, torques (Td/2)-.alpha. and (Td/2)+.alpha. are transmitted respectively to the faster and slower output shafts, in which Td means a differential case torque transmitted from an engine and .alpha. denotes a constant value inherent to the structure of the LSD.
There have also been proposed Furgason-type differential limiting devices, in each of which silicone oil or the like is filled between each two adjacent disks of a multiplicity of disks rotatable as unitary members with both output shafts and a limiting torque (equivalent to the above-described .alpha.) is applied in proportion to the difference in revolution speed between both shafts by making use of the fact that the shear force of the silicone oil increases in proportion to the difference in revolution speed between both shafts.
The former differential limiting devices (LSDs) however show their differential limiting function even when smallest differences exist in rotation speed between both shafts. When mounted on cars, they induce problems such as deterioration in driving feeling and steering stability.
On the other hand, the latter differential limiting devices (i.e., of the Furgason type) must employ many disks due to their structures, resulting in an inevitable problem that their structures become voluminous.
In addition, there is a relation between the difference .DELTA.N in revolution speed between the front and rear wheels and the produced torque T as shown by a letter C' in FIG. 6. Accordingly, a torque rises so abruptly that the tight corner braking phenomenon takes place.
Since a wet clutch has such a structure that a torque is produced by allowing its disks to slide on one another under pressure, there is a possible problem that the disks may be burnt out due to sliding friction when a large difference in revolution speed continues to exist.